Group buying has emerged as a distinctive strategy in today's product and service markets, offering low-priced products to a large number of customers. As many sellers now offer both group and individual purchasing options, this pricing model benefits both sellers and buyers, with sellers reducing prices to drive higher sales volume. In this study, we investigate the competition between two retailers selling substitutable products in the same market through both group and individual purchasing mechanisms. The profit function of duopoly retailers is represented, using a game theoretic approach to evaluate the conditions under which group buying is offered. Additionally, we address the challenge of determining individual and group prices, as well as the optimal group size. The numerical analysis reveals that in collectivist-dominated markets, where group buying is easily viable, offering group prices may not be beneficial for retailers. While, in individualist-dominant markets, retailers tend to provide both group and individual prices.
